An indole-based near-infrared fluorescent "Turn-On" probe for H₂O₂: Selective detection and ultrasensitive imaging of zebrafish gallbladder

Fluorescent probes play essential roles in medical imaging, where the researchers can select one of many molecules to use to help monitor the status of living systems under investigation. To date, a few scaffolds that allow the in vivo detection of H₂O₂ are available only. Herein, we provide a highly sensitive and selective near-infrared fluorescent probe that detects H₂O₂ based on the ICT sensing mechanism. We report the first indole-incorporated fluorescent probe Indo-H₂O₂ that allows H₂O₂ detection with a LOD of 25.2 nM featuring a boronate group conjugated to an indole scaffold; the boronate cleaves upon reaction with H₂O₂. A 5-membered malononitrile derivative was incorporated; Indo-H₂O₂ has near-infrared (NIR) properties and the reaction time is low (∼25 min) compared to other related probes. Indo-H₂O₂ was successfully employed in both endogenous and exogenous imaging trials of H₂O₂ in living cells. Indo-H₂O₂ also allows the real-time monitoring of H₂O₂in vivo. It preferentially accesses the gallbladder of zebrafish. Our findings support Indo-H₂O₂ as a highly sensitive fluorescent NIR probe for detecting H₂O₂, and an idea to incorporate a central indole unit in future fluorescent probe designs.